1. Field of the Invention
The present invention relates to a wiring board.
2. Description of the Related Art
Conventionally, in order to form a through wiring in a silicon substrate, a bottom-up plating process using a conductive layer as an electrode has been used, for example. Specifically, first, a film conductive layer is formed at a lower side of the silicon substrate. Then, copper (Cu) is deposited in a through hole provided in the silicon substrate by electrolytic plating process using the conductive layer as a seed layer (see Patent Document 1, for example).
However, in such a method, the copper (Cu) deposited in the through hole just contacts an inner side surface of the through hole but does not adhere to the inner side surface. Thus, when the silicon substrate is repeatedly used in high temperature environment or low temperature environment, pumping phenomenon of copper (expansion and contraction due to temperature variation) is generated due to the difference between coefficients of thermal expansion of silicon and copper. Then, copper is removed from the inner side surface of the through hole to cause a conductive failure of the through wiring.
In order to solve such a problem, a method of forming a through wiring is known in which an insulating layer is formed on a surface of a silicon substrate including an inner side surface of a through hole, a seed layer whose adhesion to the insulating layer is good is formed on the surface of the silicon substrate including the inner side surface of the through hole, and then the through wiring is formed in the through hole by filling plating. With this method, the pumping phenomenon of the copper may be suppressed and the likelihood that the copper is removed from the inner side surface of the through hole to cause the conductive failure of the through wiring can be reduced. However, there is a problem in that the likelihood of generation of a defect such as a seam, a void, or the like, in the through wiring is increased. The likelihood of such generation of the defect becomes high when the aspect ratio of the through hole becomes high.